1. Field of the Invention
The present invention relates to an improved semiconductor device which is suited for use as a VMIS (V-groove metal insulator semiconductor) dynamic RAM (random access memory).
2. Description of the Prior Art
There has heretofore been known a memory cell of the type of a VMIS one-transistor/cell as one type of a semiconductor memory device for use in a large-capacity highspeed RAM. In the memory cells of the VMIS-type, usually, a single V-shaped groove corresponding to a single capacitor region. Therefore, it is difficult to obtain memory cells of good quality unless exact precision is obtained to bring the capacitor region and the V-shaped groove into position during the manufacturing step.
According to another conventional example, a capacitor region is divided by a V-shaped groove to form capacitor regions on both sides of the V-shaped groove. Namely, the capacitor region formed in the shape of a column is divided by an elongated groove. With the above-mentioned construction, a single independent capacitor region is divided by a V-shaped groove to form two capacitor regions, i.e., to form two memory cells. Therefore, when the mutual arrangement of the capacitor region and the V-shaped groove is not precise, either one of the divided, embedded layers will have a small area, causing the capacitance of the capacitor of the memory cell to become smaller than a predetermined value. Since the capacitance determines an electric charge-retaining time, i.e., determines the memory-retaining characteristics related to the refreshing cycle, the minimum value must be strictly ensured. In the above-mentioned conventional examples, therefore, the area of the embedded layer must be increased by taking into consideration the deviation in position of the V-shaped groove, causing the degree of integration to be decreased. In particular, since the V-shaped groove is formed after the epitaxial layer has been grown on the embedded layer, there is not a clear pattern which helps to attain the positioning. Hence, the position of the V-shaped groove tends to be greatly varied, making the aforementioned problem more serious.